The disclosed invention relates to ink jet printing devices, and more particularly to improved techniques for driving a print carriage.
An ink jet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes called xe2x80x9cdot locations,xe2x80x9d xe2x80x9cdot positions,xe2x80x9d or xe2x80x9cpixelsxe2x80x9d. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink.
Ink jet printers print dots by ejecting very small drops of ink onto the print medium, and typically include a movable print carriage that supports one or more printheads each having ink ejecting nozzles. The print carriage is slidably supported by a slider rod and traverses back and forth over the surface of the print medium. While the print carriage moves back and forth, the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed. Typically, a plurality of rows of pixels are printed in each traverse or scan of the print carriage. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using thermal printhead or piezoelectric technology. For instance, two earlier thermal ink jet ejection mechanisms are shown in commonly assigned U.S. Pat. Nos. 5,278,584 and 4,683,481. In a thermal system, an ink barrier layer containing ink channels and ink vaporization chambers is disposed between a nozzle orifice plate and a thin film substrate. The thin film substrate typically includes arrays of heater elements such as thin film resistors which are selectively energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized heater element. By selectively energizing heater elements as the printhead moves across the print medium, ink drops are ejected onto the print medium in a pattern to form the desired image.
Typically, a print carriage is caused to move back and forth by a carriage motor that drives an endless belt attached to the carriage. Various components are attached to the carriage, and thus a consideration with attaching the drive belt to the carriage is the need for space on the carriage to accommodate the attachment structure. This imposes limits on reducing the size of the carriage, which in turn limits reduction of product size.
A further consideration with attaching a drive belt to a print carriage is the difficulty and impracticality of attaching the belt at a location that is optimal for carriage dynamic stability, since other components are also mounted on the carriage. As a result of attaching the endless belt at a non-optimal location, twisting forces are imparted to the carriage by the drive belt. Depending upon implementation, various techniques have been employed to prevent the twisting forces from affecting carriage stability. These techniques have included using sufficiently low acceleration and/or design of carriage supporting bearing structures that resist the twisting forces. Low acceleration results in slower printing and wider printers since more carriage travel is required to achieve a predetermined constant velocity, while bearing structures that are resistant to twisting forces produce more friction which requires more power to drive the carriage.
There is accordingly a need for an improved mechanism for driving a print carriage.
The disclosed invention is directed to a print carriage assembly that includes a print carriage slidably supported on a printer slider rod, and a sub-carriage that is separate from the printer carriage and slidably supported on the printer slider rod for moving the printer carriage.